1. Field of the Invention
The present invention relates to a technique by which a crystalline silicon film having a monocrystal-like region or a substantially monocrystal-like region is formed on a substrate having an insulating surface made of glass or the like. Also, the present invention relates to a technique by which a thin-film semiconductor device represented by a thin-film transistor is formed by using the crystalline silicon film.
2. Description of the Related Art
In the recent years, attention has been directed to a technique by which a thin-film transistor is constituted by using a thin-film silicon semiconductor film (a thickness of about several hundred to several thousand .ANG.) which is formed on a substrate having a glass substrate or an insulating surface. What the thin-film transistor is applied to with the most expectancy is an active matrix type liquid-crystal display unit.
The active matrix type liquid-crystal display unit is structured such that liquid crystal is interposed between a pair of glass substrates and held therebetween. Also, it is structured such that a thin-film transistor is disposed on each of pixel electrodes which are arranged in the form of a matrix of several hundred.times.several hundred. Such structures require a technique by which the thin-film transistor is formed on a glass substrate.
In the formation of the thin-film transistor on the glass substrate. it is necessary to form a thin-film semiconductor for constituting the thin-film transistor on the glass substrate. For the thin-film semiconductor formed on the glass substrate, an amorphous silicon film formed through the plasma CVD technique or the low pressure thermal CVD technique is generally utilized.
Under existing circumstances, the thin-film transistor using the amorphous silicon film is practically used. However, in order to obtain display with a higher image quality, there is demanded a thin-film transistor utilizing a silicon semiconductor thin film (called "a crystalline silicon film") with a crystalline property.
Techniques disclosed in Japanese Patent Unexamined Publication No. 6-232059 and Japanese Patent Unexamined Publication No. 6-244103 made by the present applicant have been well known as a method of forming the crystalline silicon film on the glass substrate. The techniques disclosed in those publications are that a crystalline silicon film is formed on a glass substrate through a heat treatment under a heating condition which can be withstood by the glass substrate, that is, approximately at 550.degree. C. for 4 hours, by utilizing a metal element that promotes the crystallization of silicon.
However, the crystalline silicon film obtained by the method using the above-mentioned techniques is not available to a thin-film transistor that constitutes a variety of arithmetic operating circuits, memory circuits or the like. This is because its crystalline property is insufficient and a characteristic as required is not obtained.
As the peripheral circuits of the active matrix type liquid-crystal display unit or the passive type liquid-crystal display unit, there are required a drive circuit for driving a thin-film transistor disposed in a pixel region, a circuit for dealing, with or controlling a video signal, a memory circuit for storing a variety of information etc.
Of those circuits, the circuit for dealing with or controlling a video signal and the memory circuit for storing a variety of information are required to provide a performance equal to that of an integrated circuit using a known monocrystal wafer. Hence, when those circuits are to be integrated using the thin-film semiconductor formed on the glass substrate, the crystalline silicon film having the crystalline property equal to that of monocrystal must be formed on the glass substrate.
As a method of enhancing the crystalline property of the crystalline silicon film, there have been proposed that the obtained crystalline silicon film is subjected to a re-heating treatment or to the irradiation of a laser beam. However, it has been proved that, even though the heat treatment or the irradiation of a laser beam is repeatedly conducted, it is difficult to dramatically improve the crystalline property.
Also, a technique in which a monocrystal silicon thin film is obtained by using the SOI technique has now been researched. However, since the monocrystal silicon substrate cannot be utilized for the liquid-crystal display unit, the above technique cannot be applied directly to the liquid-crystal display unit. In particular, in the case of using a monocrystal wafer, it is difficult to apply the SOI technique to the liquid-crystal display unit having a large area a demand of which is expected to increase in the future because of a limited substrate area.